Subject: Re: [RFC Patch net-next 2/4] net_sched: avoid holding qdisc lock for filters

From: John Fastabend <[email-masked]>
Date: Thu, 09 Jan 2014 19:13:42 -0800

On 01/09/2014 10:19 AM, Cong Wang wrote:
> Cc: John Fastabend <[email-masked]>
> Cc: Eric Dumazet <[email-masked]>
> Cc: David S. Miller <[email-masked]>
> Cc: Jamal Hadi Salim <[email-masked]>
> Signed-off-by: Cong Wang <[email-masked]>
> ---
>   include/net/pkt_cls.h     | 25 ++++---------------------
>   include/net/sch_generic.h |  5 +++--
>   net/sched/cls_api.c       | 12 +++++-------
>   3 files changed, 12 insertions(+), 30 deletions(-)
>
> diff --git a/include/net/pkt_cls.h b/include/net/pkt_cls.h
> index 50ea079..9afb15b 100644
> --- a/include/net/pkt_cls.h
> +++ b/include/net/pkt_cls.h
> @@ -18,26 +18,9 @@ int register_tcf_proto_ops(struct tcf_proto_ops *ops);
>   int unregister_tcf_proto_ops(struct tcf_proto_ops *ops);
>
>   static inline unsigned long
> -__cls_set_class(unsigned long *clp, unsigned long cl)
> +cls_set_class(unsigned long *clp, unsigned long cl)
>   {

commit message should mention this conversion to xchg.

> -	unsigned long old_cl;
> -
> -	old_cl = *clp;
> -	*clp = cl;
> -	return old_cl;
> -}
> -
> -static inline unsigned long
> -cls_set_class(struct tcf_proto *tp, unsigned long *clp,
> -	unsigned long cl)
> -{
> -	unsigned long old_cl;
> -	
> -	tcf_tree_lock(tp);
> -	old_cl = __cls_set_class(clp, cl);
> -	tcf_tree_unlock(tp);
> -
> -	return old_cl;
> +	return xchg(clp, cl);
>   }
>
>   static inline void
> @@ -46,7 +29,7 @@ tcf_bind_filter(struct tcf_proto *tp, struct tcf_result *r, unsigned long base)
>   	unsigned long cl;
>
>   	cl = tp->q->ops->cl_ops->bind_tcf(tp->q, base, r->classid);
> -	cl = cls_set_class(tp, &r->class, cl);
> +	cl = cls_set_class(&r->class, cl);
>   	if (cl)
>   		tp->q->ops->cl_ops->unbind_tcf(tp->q, cl);
>   }
> @@ -56,7 +39,7 @@ tcf_unbind_filter(struct tcf_proto *tp, struct tcf_result *r)
>   {
>   	unsigned long cl;
>
> -	if ((cl = __cls_set_class(&r->class, 0)) != 0)
> +	if ((cl = cls_set_class(&r->class, 0)) != 0)
>   		tp->q->ops->cl_ops->unbind_tcf(tp->q, cl);
>   }
>
> diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
> index 97123cc..000ce54 100644
> --- a/include/net/sch_generic.h
> +++ b/include/net/sch_generic.h
> @@ -215,6 +215,7 @@ struct tcf_proto_ops {
>
>   struct tcf_proto {
>   	/* Fast access part */
> +	spinlock_t		lock;

[...]

Th lock can just be dropped all these operations are initiated via
rtnetlink and hence have rtnl held.

.John
-- 
John Fastabend         Intel Corporation